1. Technical Field
The present invention relates to a method of driving an electrophoresis display device, an electrophoresis display device, and an electronic apparatus.
2. Related Art
When an electric field is applied to a dispersion solution that is obtained by dispersing electrophoresis particles in a solution, a phenomenon (electrophoresis phenomenon) where the electrophoresis particles migrate due to a Coulomb force is generated. An electrophoresis display device such as a piece of electronic paper using the electrophoresis phenomenon has been developed.
Each of the electrophoresis display devices includes pixel electrode provided for each of a plurality of pixels and a common electrode that is commonly provided opposite to the plurality of pixel electrodes and is driven to make the electrophoresis particles migrate by using an electric field generated by a potential difference between the pixel electrodes and the common electrode. In the electrophoresis display device, a state where the electrophoresis particles migrate by the driving method described above is displayed as a display image.
In addition, as a representative driving method in a display device such as a liquid crystal display, a driving method so-called “common oscillation driving” where a potential of each of the pixel electrode is switched and a potential of the common electrode is also switched is known. In addition, a technique for applying the common oscillation driving to the electrophoresis display device has been suggested (see, JP-A-52-70791).
According to the technique disclosed in JP-A-52-70791, by the common oscillation driving, the potential of the pixel electrodes and the common electrode can be controlled in two values that are a high potential and a low potential, and thereby voltage reduction of the electrophoresis display device can be realized. In addition, the electrophoresis display device can be produced at a low cost to have a simple circuit configuration. In addition, in a case where a TFT (Thin Film Transistor) is used as a driving circuit of the electrophoresis display device, since a low-voltage driving may be realized, it is possible to secure reliability of the TFT.
In addition, there is disclosed a circuit where a memory cell is provided to each of the pixels, such that it is possible to store data written to each of the pixels (see JP-A-58-143389). In a pixel driving circuit having such a circuit configuration, when data to be written to the pixel is the same to that written already, it is unnecessary to transfer the data to the pixel, such that it is possible to stop a periphery circuit, and thereby it is possible to expect a remarkable decrease in power consumption.
Here, description will be given with respect to the common oscillation driving. FIG. 10 shows an example of a timing chart of the common oscillation driving in the electrophoresis display device of the related art. First, prior to the description with reference to FIG. 10, the electrophoresis display device is assumed as described below. First, each of the pixels in the electrophoresis display device is configured by a plurality of microcapsules including white electrophoresis particles (hereinafter, referred to as “white particles”) and black electrophoresis particles (hereinafter, referred to as “black particles”). In addition, in each of the microcapsules, the black particles are charged with a positive polarity (plus: +) and the white particles are charged with a negative polarity (minus: −). In this case, in a case where the pixel electrode is maintained at a high potential (for example, 10 V), when a potential of the common electrode is maintained at a low potential, the black particles in the microcapsule electrically migrate to the common electrode side and thereby a black color is displayed by the pixel. In addition, in a case where the pixel electrode is maintained at a low potential (for example, 0 V), when a potential of the common electrode is maintained at a high potential, the white particles in the microcapsule electrically migrate to the common electrode side and thereby a white color is displayed by the pixel.
In addition, in a case where the potential of the pixel electrode and the common electrode are the same (both are at a low potential or a high potential), the black particles or the white particles in the microcapsule do not electrically migrate and thereby the present display state is maintained.
With respect to the timing of the common oscillation driving in the electrophoresis display device of the related art, as shown in FIG. 10, in a display set-up period, data for a black display is written to a memory cell of a pixel (for example, a pixel B of FIG. 10) for displaying a black color and data for a white display is written to a memory cell of a pixel (a pixel W of FIG. 10) for displaying a white color. In the display set-up period, the potential of all the pixel electrodes is allowed to be equal to that of the common electrode. Then, in a display rewrite period, the potential of the pixel electrode of each of the pixels is changed according to the written data and a potential VCOM of the common electrode is periodically changed to a high potential or a low potential. Therefore, due to an electric field generated in the microcapsule in each of the pixels by a potential difference between the pixel electrode and the common electrode, a black display and a white display are alternately written to each of the pixels. As described above, the potential VCOM of the common electrode is periodically selected from the high potential and the low potential and thereby writing is performed to each of the pixels, such that an image corresponding to written data is displayed to the electrophoresis display device.
As described above, in the electrophoresis display device, the black particles or the white particles alternately electrically migrate according to the potential of the pixel electrode and the potential VCOM of the common electrode and thereby a black color or a white color is displayed in each of the pixels. In the common oscillation driving, when a cycle (potential selection cycle) of periodically selecting the potential VCOM of the common electrode into a high potential and a low potential becomes rapid, there is an advantage that the human eye perceives as if a black color and a white color are concurrently written, despite that a pixel where a black color is displayed and a pixel where a white color is displayed are actually alternately changed.
As described above, two kinds of electrophoresis particles including black particles for displaying a black color and white particles for displaying a white color are present in an electrophoresis display device. A migration speed when the white particles electrically migrate and a migration speed when the black particles electrically migrate in a microcapsule may not be equal, and may be different between the black particles and the white particles.
For example, it is assumed that the migration speed of the white particles is fast, and the migration speed of the black particles is slow. At this time, in a case where a writing time of a pixel by a common oscillation driving is determined depending on a characteristic of the migration speed of the white particles, the electrophoresis of the black particles of which the migration speed is slow becomes insufficient, and thereby the black color may be insufficiently displayed. In addition, on the contrary, in a case where the writing time of the pixel by the common oscillation driving is determined depending on a characteristic of the migration speed of the black particles, writing with respect to the pixel where the white color is displayed becomes excessive and thereby the reliability of the electrophoresis display device may be lowered.
Therefore, in the common oscillation driving of the related art, there is a problem that the characteristics of a migration speed of the electrophoresis particles are not considered.